The amino acid sequence of beta-galactosidase of the Lactose Operon of Escherichia coli will be determined by methods of protein chemistry. Beta-Galactosidase polypeptides produced by mutant strains of bacteria are being isolated to aid sequence work and to extend gene-protein relationships. Complementation of beta-galactosidase fragments is being investigated. The primary structure of thiogalactoside transacetylase will also be determined.